This invention relates to a device for holding paper close against a corrugating roller in a corrugated board-making machine.
As it is known, current corrugated board-making machines, or corrugating machines, have a main body accommodating three large diameter rollers which are laid side-by-side and in mutual serial engagement relationship. Two of such rollers are corrugated, whereas the third roller is smooth. Paper to be corrugated enters the nip between the corrugated rollers and is partly trained over the middle corrugated roller constituting the corrugating roller proper. On leaving said corrugating roller, the paper workpiece, now corrugated, is joined to a second, smooth paper sheet, called the cover, which is born by the smooth roller.
Prior to this step, while the paper to be corrugated is still on the corrugating roller, a glueing roller applies an amount of glue over the paper surface.
Corrugating machines of that type are highly sophisticated equipments capable of operating at a very high speed: as an example, they may be operated to produce a 200-meter long strip of corrugated board per minute.
Critical to the processing rate and quality of such machines is the construction of the corrugating roller and proper operation of devices located at the corrugating roller and intended for holding the paper being corrugated close against that roller. In fact, at such high rates of operation, the high angular velocity of the corrugating roller subjects the paper to be corrugated and trained over it to a centrifugal action tending to lift the paper radially off, thus separating it from the corrugations or ribs which are to mold it. To prevent this occurrence, which is a cause for serious deterioration of the quality of the corrugated board product and simultaneously avoid lowering the corrugating roller rotational speed, corrugating machines have been equipped with some special devices, which form the specific subject matter of this invention.
Such devices, which are essential to the proper operation of corrugating machines, have undergone several design and construction changes as the engineering and performance of corrugating machines kept evolving.
At the outset, they were in the form of simple semi-circular brass segments, called combs, which were set to skim the crests of the wave pattern on the middle roller and resist separation of the corrugated paper. These semi-circular segments or combs have the disadvantage of hindering to an extent the action of the cited glueing roller, and above all, of being inadequate to keep the paper close against the corrugating rollers as the latter are rotated at a high angular velocity owing to their much limited coverage.
Thus, new and more efficient devices have been developed which hold the paper against the corrugating rollers by drawing it through suction holes and conduits formed in the corrugating roller itself, or drawing it on the opposite side to where the combs were conventionally installed.
Suction drawing through holes and conduits formed through the corrugating roller has in many cases shown to be inadequate, and it seriously interferes with the heating effect applied by the roller to the paper. It should be made clear, in fact, that the corrugating roller is, similarly to the rollers adjoining it, of hollow construction, and through its center cavity, high temperature steam is admitted for heating the corrugating roller and, accordingly, the paper wound around it. It has been found that if the paper is embossed at a high temperature, the corrugations are of improved quality and more stable.
It is apparent that suction drawing, carried out by means of channels extending through the interior of the corrugating roller decreases said heating effect and causes serious distortion of the corrugating roller.
The suction devices which operate on the outside of the corrugating roller, on the opposite side to that where the paper is wound and where combs were conventionally installed, do not suffer from the disadvantage of cooling the roller and inducing distortion therein, since the suction action only affects the surface and is applied on the corrugating cylinder side which is not directly engaged with the paper. However, this technical approach retains the serious disadvantage of a poor effectiveness of the suction which must reach the paper being corrugated. To remedy this problem, circular cutouts have been made in the surface shroud of the middle roller, which are specially thin not to interfere with the embossing of the corrugated paper. Through such cutouts or grooves, the paper is suction drawn and held close against the corrugating roller through an arc of about 180 degrees.
The latter approach has shown to be suitable for processing rates resulting in the attainment of the cited output of 200 meter corrugated paper per minute. At higher rates, and accordingly higher angular velocities of the corrugating roller rotation, the suction effect shows to be inadequate. In view of the constant present trend toward higher processing rates with corrugating machines, attempts have already been made at obviating this deficiency by making the suction effect more effective through the use of small size spouts arranged to be active directly level with the grooves or indentations of the corrugating roller. Thus, the suction effect has been made more directly applied, and it has shown to be theoretically adequate even though the vacuum pumps currently producing it are obliged to operate at the upper limit of their capability. However, with the latter approach, other shortcomings of those devices which hold the corrugated paper down by suction drawing have shown to still exist and be aggravated.
As an example, the danger of clogging the suction outlets by the paper fragments released during the corrugating step is increased. Further, the suction effect becomes heavily dependent on the width dimension of the paper strip being corrugated: any decrease in the width dimension would leave lateral regions of the corrugating roller exposed, thus allowing air freely into the suction ports.
The most serious drawback, connected with the use of suction spouts which act directly level with the circular indentations on the corrugating roller, is foreign, however, to the foregoing and as follows.
In the transition from the inoperative step to the operative one, the corrugating roller expands considerably, both radially and longitudinally, as a consequence of the cited heat applied by the steam flow through its center cavity. This expansion affects said spouts by twisting them and forcing them into contact interaction with the walls of said grooves. This results, inter alia, in premature wear of the spouts and consequent need for applying a constant and careful maintenance to the corrugating machine.
It should be plain from the foregoing that currently available devices for holding corrugated paper are, in many ways, unsatisfactory, and already exploited to the limit of their capabilities.